The production of ceramic articles in general and of abrasive grain in particular by the use of seeded gels has been demonstrated as in U.S. Pat. No. 4,623,364. By virtue of the intrinsic small particle size of the gel particles (less than 0.1 micron), and the facilitation, by the inclusion of nucleating seeds, of the conversion to alpha alumina, unique and valuable sintered bodies may be produced. Low sintering temperatures (e.g. 1200.degree.-1400.degree. C.), very fine microstructures (grain size less than 0.5 microns) and high density are realized when seeded gels are utilized. It has been further shown that such ceramic bodies are extremely good abrasive materials in many applications, often outperforming premium fused alumina or alumina-zirconia abrasives by a factor of 2 to 10 or more. The extremely fine crystal structure achievable by this process also allows the production of shaped alpha alumina bodies having substantially improved properties.
Micro crystalline boehmite is also useful for making porous gamma alumina bodies, e.g. for catalytic applications. All of these applications require boehmite having very fine particle sizes, generally less than 300 Angstroms, and preferably less than 100 or even 50 Angstroms in many applications.
The major disadvantage of the sol-gel abrasives currently is the high cost of the microcrystalline boehmite starting material. Because of this, the final product is costly and so markets are restricted to relatively specialized applications where relative performance/value is optimized. It is very desirable to increase the markets by lowering the cost of the abrasive by finding an economical source of microcrystalline boehmite and microcrystalline boehmite gels.
The availability of a low cost source of microcrystalline boehmite and microcrystalline gels would also be of great importance in making shaped alumina bodies such as porous gamma alumina bodies (e.g. for catalytic applications) and alpha alumina bodies such as structural parts and catalyst carriers.
Commercial production of such boehmite gels or gel precursors at present arises from two basic sources: (1) hydrolysis of high purity aluminum alkoxides, and, (2) precipitation from solutions of sodium aluminate. High costs arise from these methods because (a) users desire high purity material (hence expensive high purity materials or aluminum metal are used as a starting material) or distillation is performed or extensive washing is required, (b) loss of chemical reagents occurs (alcohol, sodium, salts, etc.), (c) elaborate safety precautions must be taken because of the use of flammable liquids or corrosive solutions, (d) low production rates are often encountered in certain processes since the gelability of boehmite is very sensitive to kinetics of precipitating, washing and drying.
Microcrystalline boehmite is normally supplied by manufacturers in powdered form and must be dispersed in water to form a sol. Since the manufacturer of the microcrystalline boehmite initially required drying the material to form the powder, substantial energy savings could be achieved if the drying step could be avoided.
It follows then, that by reducing or eliminating disadvantages such as listed above, significant cost advantages can be achieved.